Sapphire thin film coated flexible substrate

ABSTRACT

A method to transfer a layer of harder thin film substrate onto a softer, flexible substrate. In particular, the present invention provides a method to deposit a layer of sapphire thin film on to a softer and flexible substrate e.g. PET, polymers, plastics, paper and fabrics. This combination provides the hardness of sapphire thin film to softer flexible substrates.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of: (1) U.S.Non-Provisional patent application Ser. No. 14/642,742 filed on Mar. 9,2015 which claims priority from U.S. Provisional Patent Application Ser.No. 62/049,364 filed on Sep. 12, 2014, and (2) U.S. Non-Provisionalpatent application Ser. No. 13/726,127 filed on Dec. 23, 2012 whichclaims priority from U.S. Provisional Patent Application Ser. No.61/579,668 filed on Dec. 23, 2011, and (3) U.S. Non-Provisional patentapplication Ser. No. 13/726,183 filed on Dec. 23, 2012 which claimspriority from U.S. Provisional Patent Application Ser. No. 61/579,668filed on Dec. 23, 2011. This application also claims priority from U.S.Provisional Patent Application Ser. No. 62/183,182 filed on Jun. 22,2015, and U.S. Provisional Patent Application Ser. No. 62/049,364 filedon Sep. 12, 2014. The disclosures of all the above referenced patentapplications are hereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to a method to transfer a layer of harderthin film substrate onto a softer substrate, especially onto a softer,flexible substrate. In particular, the present invention provides amethod to transfer a layer of sapphire thin film on to a softer flexiblesubstrate e.g. PET, polymer, plastic, paper and fabric via a flip chipprocess. The combination of a layer of harder thin film sapphiresubstrate onto a softer substrate is better than pure sapphiresubstrate. In nature, the harder the materials, the more fragile theyare, thus, sapphire substrate is hard to scratch but it is easy toshatter, and the vice versa is also often true wherein quartz substrateis easier to scratch but it is less fragile than sapphire substrate.Therefore, depositing a harder thin film substrate on a softer, flexiblesubstrate gives the best of both worlds. Softer, flexible substrates areless fragile, have good mechanical performance and often cost less. Thefunction of anti-scratch is to achieve by using the harder thin filmsubstrate.

BACKGROUND OF THE INVENTION

Sapphire is presently being actively considered as screen for smartphones and tablets. It is second hardest material after diamond so usingit as screen would mean the smart phone/tablet has a superior scratchand crack resistant screen. Sapphire screen is already being featured oniPhone 5S TouchID scanner and camera lens on the rear of the phone.Vertu, the luxury smartphone manufacturer is also developing sapphirescreen. However, since sapphire is the second hardest material, it isalso difficult to be cut and polished. Coupled by the fact that thegrowth of a large size of single crystal sapphire is time consuming,this results in long fabrication time and high fabrication cost. Thehigh fabrication cost and long fabrication time of sapphire screen limitthe Apple Inc. use of such sapphire screen only for Apple Watch.

Current popular ‘tough’ screen material use is Gorilla Glass fromCorning which is being used in over 1.5 billion devices. Sapphire is infact harder to scratch than Gorilla Glass and this is being verified byseveral third party institutes such as Center for Advanced CeramicTechnology at Alfred University's Kazuo Inamori School of Engineering.On the Mohs scale of hardness, the newest Gorilla Glass only scores 6.5Mohs which is below the Mohs value of mineral quartz such that GorillaGlass is still easy to be scratched by sand and metals. Sapphire is thesecond hardest naturally occurring material on the planet, behinddiamond which scores 10 on the Mohs scale of mineral hardness. This testmatches one substance's ability to scratch another—and so it is a betterindicator of scratch resistance than shatter resistance.

Mohs hardness test is to characterize the scratch resistance of mineralsthrough the ability of a harder material to scratch a softer material.It matches one substance's ability to scratch another, and so is abetter indicator of scratch resistance than shatter resistance. This isshown in FIG. 1.

Following is quotations from ‘Display Review’ on sapphire screen:

-   -   “Chemically strengthened glass can be excellent, but sapphire is        better in terms of hardness, strength, and toughness” Hall        explained adding “the fracture toughness of sapphire should be        around four times greater than Gorilla Glass—about 3 MPa-m0.5        versus 0.7 MPa-m0.5, respectively.”        This comes with some rather large downsides though. Sapphire is        both heavier at 3.98 g per cubic cm (compared to the 2.54 g of        Gorilla Glass) as well as refracting light slightly more.

So apart from being heavier, sapphire being second hardest material isalso difficult material to cut and polish. Growing single crystalsapphire is time consuming especially when the diameter size is large(>6 inches), this is technically very challenging. Therefore thefabrication cost is high and fabrication time is long for sapphirescreen. It is an objective of the present invention to providefabrication means of sapphire screen materials that is quick tofabricate and low in cost while having the following advantages:

-   -   Harder than any hardened glass;    -   Less possibility of fragmentation than pure sapphire screen;    -   Lighter weight than pure sapphire screen;    -   Higher transparency than pure sapphire screen.        For hardening of sapphire (Al₂O₃) thin film deposition,        softening/melting temperature of softer substrate should be        sufficiently higher than the annealing temperature. Most rigid        substrates such as quartz, fused silica can meet this        requirement. However flexible substrate such as polyethylene        terephthalate (PET) would not be able to meet the requirement.        PET has a melting temperature of about 250° C., which is well        below the annealing temperature. PET is one of the most widely        used flexible substrates. The ability of transferring a        substrate of Al₂O₃ (sapphire) thin films on to a softer flexible        will significantly broaden its applications from rigid        substrates like glass and metals to flexible substrates like        PET, polymers, plastics, paper and even to fabrics. Mechanical        properties of transferred substrate can then be improved.        Therefore, Al₂O₃ thin films transfer from rigid substrate to        flexible substrate can circumnavigate this problem of the often        lower melting temperatures of flexible substrates.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, there isprovided a method to transfer a layer of harder thin film substrate ontoa softer, flexible substrate. In particular, the present inventionprovides a method to transfer a layer of sapphire thin film onto asofter, flexible substrate e.g. PET, polymers, plastics, paper and evento fabrics. This combination is better than pure sapphire substrate.

In accordance with a second aspect of the present invention, there isprovided a method for coating sapphire (Al₂O₃) onto flexible substratecomprising

-   -   at least one first deposition process to deposit at least one        first thin film onto at least one first substrate to form at        least one first thin film coated substrate;    -   at least one second deposition process to deposit at least one        second thin film onto the at least one first thin film coated        substrate to form at least one second thin film coated        substrate;    -   at least one third deposition process to deposit at least one        catalyst onto the at least one second thin film coated substrate        to form at least one catalyst coated substrate;    -   at least one fourth deposition process to deposit at least one        sapphire (Al₂O₃) thin film onto the at least one catalyst coated        substrate to form at least one sapphire (Al₂O₃) coated        substrate;    -   at least one annealing process, wherein said at least one        sapphire (Al₂O₃) coated substrate is annealed under an annealing        temperature ranging from 300° C. to less than a melting point of        sapphire (Al₂O₃) for an effective duration of time to form at        least one harden sapphire (Al₂O₃) thin film coated substrate;    -   attaching at least one flexible substrate to the at least one        harden sapphire (Al₂O₃) thin film coated substrate on the at        least one sapphire (Al₂O₃) thin film;    -   at least one mechanical detachment process detaching the at        least one harden sapphire (Al₂O₃) thin film together with the at        least one second thin film from the at least one first thin film        coated substrate to form at least one second thin film coated        harden sapphire (Al₂O₃) thin film on said at least one flexible        substrate; and    -   at least one etching process removing the at least one second        thin film from the at least one second thin film coated harden        sapphire (Al₂O₃) thin film on said at least one flexible        substrate to form at least one sapphire (Al₂O₃) thin film coated        flexible substrate.

The method according to claim 1, wherein said first and/or said flexiblesubstrate comprises at least one material with a Mohs value less thanthat of said deposit at least one sapphire (Al₂O₃) thin film.

In a first embodiment of the second aspect of the present inventionthere is provided the method wherein said at least one first and/orsecond and/or third and/or fourth deposition process comprises e-beamdeposition and/or sputtering deposition.

In a second embodiment of the second aspect of the present inventionthere is provided the method wherein said at least one sapphire (Al₂O₃)coated substrate and/or at least one harden sapphire (Al₂O₃) coatedsubstrate and/or at least one second thin film coated harden sapphire(Al₂O₃) thin film on said at least one flexible substrate and/or atleast one sapphire (Al₂O₃) thin film coated flexible substrate comprisesat least one sapphire (Al₂O₃) thin film.

In a third embodiment of the second aspect of the present inventionthere is provided the method wherein a thickness of said at least onefirst substrate and/or said at least one flexible substrate is of one ormore orders of magnitude greater than the thickness of said at least onesapphire (Al₂O₃) thin film.

In a fourth embodiment of the second aspect of the present inventionthere is provided the method wherein the thickness of said at least onesapphire (Al₂O₃) thin film is about 1/1000 of the thickness of said atleast one first substrate and/or said at least one flexible substrate.

In a fifth embodiment of the second aspect of the present inventionthere is provided the method wherein said at least one sapphire (Al₂O₃)thin film has the thickness between 150 nm and 600 nm.

In a sixth embodiment of the second aspect of the present inventionthere is provided the method wherein said effective duration of time isno less than 30 minutes.

In an eighth embodiment of the second aspect of the present inventionthere is provided the method wherein said effective duration of time isno more than 2 hours.

In a ninth embodiment of the second aspect of the present inventionthere is provided the method wherein said annealing temperature rangesbetween 850° C. and 1300° C.

In a tenth embodiment of the second aspect of the present inventionthere is provided the method wherein said annealing temperature rangesbetween 1150° C. and 1300° C.

In an eleventh embodiment of the second aspect of the present inventionthere is provided the method wherein said at least one materialcomprising quartz, fused silica, silicon, glass, toughen glass, PET,polymers, plastics, paper and/or fabric further wherein said materialfor the at least one flexible substrate is not etch-able by the at leastone etching process.

In a twelfth embodiment of the second aspect of the present inventionthere is provided the method wherein said attachment between said atleast one flexible substrate and said at least one harden sapphire(Al₂O₃) thin film is stronger than the bonding between said at least onefirst thin film and said second thin film.

In a thirteenth embodiment of the second aspect of the present inventionthere is provided the method wherein the at least one first thin filmcomprising chromium (Cr) or any material that forms a weaker bondbetween the at least one first thin film and the at least one secondthin film further wherein said material for the first thin film is notetch-able by the at least one etching process.

In a fourteenth embodiment of the second aspect of the present inventionthere is provided the method wherein the at least one second thin filmcomprising silver (Ag) or any material that forms a weaker bond betweenthe at least one first thin film and the at least one second thin filmfurther wherein said material for the second thin film is etch-able bythe at least one etching process.

In a fifteenth embodiment of the second aspect of the present inventionthere is provided the method wherein said at least one catalystcomprises a metal selected from a group consisting of titanium (Ti),chromium (Cr), nickel (Ni), silicon (Si), silver (Ag), gold (Au),germanium (Ge) and metal with a higher melting point than the at leastone first substrate.

In a sixteenth embodiment of the second aspect of the present inventionthere is provided the method wherein said at least one catalyst coatedsubstrate comprising at least one catalyst film; wherein said at leastone catalyst film is not continuous; wherein said at least one catalystfilm has a thickness ranging between 1 nm and 15 nm; and wherein said atleast one catalyst film comprising a nano-dot with a diameter rangingbetween 5 nm and 20 nm.

Those skilled in the art will appreciate that the invention describedherein is susceptible to variations and modifications other than thosespecifically described.

The invention includes all such variation and modifications. Theinvention also includes all of the steps and features referred to orindicated in the specification, individually or collectively, and anyand all combinations or any two or more of the steps or features.

Other aspects and advantages of the invention will be apparent to thoseskilled in the art from a review of the ensuing description.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention willbecome apparent from the following description of the invention, whentaken in conjunction with the accompanying drawings.

FIG. 1 shows the Mohs scale of mineral hardness.

FIG. 2 shows the top-surface hardness of “Sapphire thin film on Quartz”when compared to ordinary glass, Gorilla Glass, quartz and puresapphire.

FIG. 3 shows the light transmittance of quartz, Sapphire thin film onQuartz and pure sapphire.

FIG. 4 shows the light transmission of quartz and 190 nm Sapphire thinfilm on Quartz with and without annealing at 1300° C. for 2 hours.

FIG. 5 shows XRD results for the 400 nm sapphire thin film on quartzannealed at 750° C., 850° C. and 1200° C. for 2 hours.

FIG. 6 shows the transmission spectrum of 400 nm sapphire thin film onquartz by e-beam with and without annealing at 1200° C. for 2 hourscomparing with quartz and sapphire substrates.

FIG. 7 shows the transmission spectrum of 160 nm sapphire thin film onfused silica by e-beam with and without annealing at 1150° C. for 2hours comparing with quartz and sapphire substrates.

FIG. 8A shows XRD results for the 400 nm sapphire thin film on quartzprepared by sputtering deposition and annealing at 850° C., 1050° C. and1200° C. for 2 hours.

FIG. 8B shows XRD results for the sapphire thin film with thicknesses of220 nm, 400 nm and 470 nm on quartz prepared by sputtering depositionand annealing at 1150° C. for 2 hours.

FIG. 9 shows the transmission spectra of 220 nm, 400 nm and 470 nmsapphire thin film on quartz by sputtering deposition and annealing at1100° C. for 2 hours comparing with quartz substrate.

FIG. 10 shows XRD results for the 350 nm sapphire thin film on fusedsilica prepared by sputtering deposition and annealing at 750° C., 850°C., 1050° C. and 1150° C. for 2 hours.

FIG. 11 shows the transmission spectra of 180 nm-600 nm sapphire thinfilm on fused silica by sputtering deposition and annealing at 1150° C.for 2 hours comparing with fused silica substrate.

FIG. 12 shows the transmission of fused silica and 250 nm annealedsapphire thin film with or without 10 nm Ti catalyst on fused silicaannealing at 700° C. and 1150° C. for 2 hours.

FIG. 13 (A) shows the X-ray reflectivity (XRR) measurement results fordifferent samples with different annealing conditions.

FIG. 13 (B) shows the optical transmittance spectra for differentsamples with different annealing conditions.

FIG. 14 shows, from (a) to (e), the five EBL steps in the fabrication ofthe absorber metamaterials with period of the disc-array device is 600nm, disc diameter: 365 nm, thickness of gold: 50 nm, and thickness ofCr: 30 nm; and shows (f) the scanning electron microscope (SEM) image ofthe two dimensional gold disc-array absorber metamaterials.

(Deleted)

FIG. 15 shows, from (a) to (e), the schematic diagrams illustrating thefive steps of the flip chip transfer method, the tri-layer absorbermetamaterial with an area of 500 μm by 500 μm was transferred to a PETflexible substrate.

FIG. 16 shows, in the insets (a) and (b), the two views of the flexibleNIR absorber metamaterials on a transparent PET substrate; eachseparated pattern has an area size of 500 μm by 500 μm.

FIG. 17 shows the relative reflection spectrum of the absorbermetamaterials on quartz substrate (gold disc/ITO/gold/Cr/quartz), NIRlight was normally focused on the device and the reflection signal andwas collected by the 15× objective lens, and blue line is theexperimental result and red line is the simulated reflection spectrumusing RCWA method.

FIG. 18 shows: (a) Angle resolved back reflection spectra measured onflexible metamaterial (with curved surface), the light being incidentfrom PET side and the back reflection was collected by NIR detector; (b)transmission spectra measured on the flexible absorber metamaterial, thelight being incident from the PMMA side was collected from the PET side;and (c) and (d) are simulated reflection and transmission spectra onflexible absorber metamaterial using RCWA method.

FIG. 19 shows experiment diagram of measuring the reflection spectrum ofmetamaterial device under different bending condition; the flexiblesubstrate was bent by adjusting the distance between A and B, and theincident angle 90°-ø (varying from 0 to 45 degree) was defined by theslope of PET substrate and direction of incident light.

FIG. 20 shows the fabrication structure for Al₂O₃ thin film transfer.

FIG. 21 shows the peeling off of Al₂O₃ thin film from the donorsubstrate.

FIG. 22 shows the etching of sacrificial Ag layer to complete the Al₂O₃thin film transfer to PET substrate.

FIG. 23 shows the fabrication sample of Al₂O₃ assembly ready for thinfilm transfer.

FIG. 24 shows the separation of Al₂O₃ from donor substrate.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is not to be limited in scope by any of thespecific embodiments described herein. The following embodiments arepresented for exemplification only.

Without wishing to be bound by theory, the inventors have discoveredthrough their trials, experimentations and research that to accomplishthe task of transferring a layer of harder thin film substrate onto asofter, flexible substrate e.g. PET, polymers, plastics, paper and evento fabrics. This combination is better than pure sapphire substrate. Innature, the harder the materials, the more fragile they are, thus,sapphire substrate is hard to scratch but it is easy to shatter, and thevice versa is also often true wherein quartz substrate is easier toscratch but it is less fragile than sapphire substrate. Therefore,depositing a harder thin film substrate on a softer, flexible substrategives the best of both worlds. Softer, flexible substrates are lessfragile, have good mechanical performance and cost less. The function ofanti-scratch is to achieve by using the harder thin film substrate. Forhardening of sapphire (Al₂O₃) thin film deposition, softening/meltingtemperature of softer substrate should be sufficiently higher than theannealing temperature. Most rigid substrates such as quartz, fusedsilica can meet this requirement. However flexible substrate such aspolyethylene terephthalate (PET) would not be able to meet therequirement. PET has a melting temperature of about 250° C., which iswell below the annealing temperature. PET is one of the most widely usedflexible substrates. The ability of transferring a substrate of Al₂O₃(sapphire) thin films on to a softer flexible will significantly broadenits applications from rigid substrates like glass and metals to flexiblesubstrates like PET, polymers, plastics, paper and even to fabrics.Mechanical properties of transferred substrate can then be improved.Therefore, Al₂O₃ thin films transfer from rigid substrate to flexiblesubstrate can circumnavigate this problem of the often lower meltingtemperatures of flexible substrates.

In accordance with a first aspect of the present invention, there isprovided a method to coat/deposit/transfer a layer of harder thin filmsubstrate onto a softer substrate. In particular, the present inventionprovides a method to deposit a layer of sapphire thin film onto a softerflexible substrate e.g. PET, polymers, plastics, paper and fabrics. Thiscombination is better than pure sapphire substrate.

In accordance with a second aspect of the present invention, there isprovided a method for coating sapphire (Al₂O₃) onto flexible substratecomprising

-   -   at least one first deposition process to deposit at least one        first thin film onto at least one first substrate to form at        least one first thin film coated substrate;    -   at least one second deposition process to deposit at least one        second thin film onto the at least one first thin film coated        substrate to form at least one second thin film coated        substrate;    -   at least one third deposition process to deposit at least one        catalyst onto the at least one second thin film coated substrate        to form at least one catalyst coated substrate;    -   at least one fourth deposition process to deposit at least one        sapphire (Al₂O₃) thin film onto the at least one catalyst coated        substrate to form at least one sapphire (Al₂O₃) coated        substrate;    -   at least one annealing process, wherein said at least one        sapphire (Al₂O₃) coated substrate is annealed under an annealing        temperature ranging from 300° C. to less than a melting point of        sapphire (Al₂O₃) for an effective duration of time to form at        least one harden sapphire (Al₂O₃) thin film coated substrate;    -   attaching at least one flexible substrate to the at least one        harden sapphire (Al₂O₃) thin film coated substrate on the at        least one sapphire (Al₂O₃) thin film;    -   at least one mechanical detachment process detaching the at        least one harden sapphire (Al₂O₃) thin film together with the at        least one second thin film from the at least one first thin film        coated substrate to form at least one second thin film coated        harden sapphire (Al₂O₃) thin film on said at least one flexible        substrate; and    -   at least one etching process removing the at least one second        thin film from the at least one second thin film coated harden        sapphire (Al₂O₃) thin film on said at least one flexible        substrate to form at least one sapphire (Al₂O₃) thin film coated        flexible substrate.

The method according to claim 1, wherein said first and/or said flexiblesubstrate comprises at least one material with a Mohs value less thanthat of said deposit at least one sapphire (Al₂O₃) thin film.

In a first embodiment of the second aspect of the present inventionthere is provided the method wherein said at least one first and/orsecond and/or third and/or fourth deposition process comprises e-beamdeposition and/or sputtering deposition.

In a second embodiment of the second aspect of the present inventionthere is provided the method wherein said at least one sapphire (Al₂O₃)coated substrate and/or at least one harden sapphire (Al₂O₃) coatedsubstrate and/or at least one second thin film coated harden sapphire(Al₂O₃) thin film on said at least one flexible substrate and/or atleast one sapphire (Al₂O₃) thin film coated flexible substrate comprisesat least one sapphire (Al₂O₃) thin film.

In a third embodiment of the second aspect of the present inventionthere is provided the method wherein a thickness of said at least onefirst substrate and/or said at least one flexible substrate is of one ormore orders of magnitude greater than the thickness of said at least onesapphire (Al₂O₃) thin film.

In a fourth embodiment of the second aspect of the present inventionthere is provided the method wherein the thickness of said at least onesapphire (Al₂O₃) thin film is about 1/1000 of the thickness of said atleast one first substrate and/or said at least one flexible substrate.

In a fifth embodiment of the second aspect of the present inventionthere is provided the method wherein said at least one sapphire (Al₂O₃)thin film has the thickness between 150 nm and 600 nm.

In a sixth embodiment of the second aspect of the present inventionthere is provided the method wherein said effective duration of time isno less than 30 minutes.

In an eighth embodiment of the second aspect of the present inventionthere is provided the method wherein said effective duration of time isno more than 2 hours.

In a ninth embodiment of the second aspect of the present inventionthere is provided the method wherein said annealing temperature rangesbetween 850° C. and 1300° C.

In a tenth embodiment of the second aspect of the present inventionthere is provided the method wherein said annealing temperature rangesbetween 1150° C. and 1300° C.

In an eleventh embodiment of the second aspect of the present inventionthere is provided the method wherein said at least one materialcomprising quartz, fused silica, silicon, glass, toughen glass, PET,polymers, plastics, paper and/or fabric further wherein said materialfor the at least one flexible substrate is not etch-able by the at leastone etching process.

In a twelfth embodiment of the second aspect of the present inventionthere is provided the method wherein said attachment between said atleast one flexible substrate and said at least one harden sapphire(Al₂O₃) thin film is stronger than the bonding between said at least onefirst thin film and said second thin film.

In a thirteenth embodiment of the second aspect of the present inventionthere is provided the method wherein the at least one first thin filmcomprising chromium (Cr) or any material that forms a weaker bondbetween the at least one first thin film and the at least one secondthin film further wherein said material for the first thin film is notetch-able by the at least one etching process.

In a fourteenth embodiment of the second aspect of the present inventionthere is provided the method wherein the at least one second thin filmcomprising silver (Ag) or any material that forms a weaker bond betweenthe at least one first thin film and the at least one second thin filmfurther wherein said material for the second thin film is etch-able bythe at least one etching process.

In a fifteenth embodiment of the second aspect of the present inventionthere is provided the method wherein said at least one catalystcomprises a metal selected from a group consisting of titanium (Ti),chromium (Cr), nickel (Ni), silicon (Si), silver (Ag), gold (Au),germanium (Ge) and metal with a higher melting point than the at leastone first substrate.

In a sixteenth embodiment of the second aspect of the present inventionthere is provided the method wherein said at least one catalyst coatedsubstrate comprising at least one catalyst film; wherein said at leastone catalyst film is not continuous; wherein said at least one catalystfilm has a thickness ranging between 1 nm and 15 nm; and wherein said atleast one catalyst film comprising a nano-dot with a diameter rangingbetween 5 nm and 20 nm.

Definitions

For clarity and completeness the following definition of terms used inthis disclosure:

The word “sapphire” when used herein refers to the material or substratethat is also known as a gemstone variety of the mineral corundumincluding those with different impurities in said material or substrate,an aluminium oxide (alpha-Al₂O₃), or alumina. Pure corundum (aluminumoxide) is colorless, or corundum with ˜0.01% titanium. The varioussapphire colors result from the presence of different chemicalimpurities or trace elements are:—

-   -   Blue sapphire is typically colored by traces of iron and        titanium (only 0.01%).    -   The combination of iron and chromium produces yellow or orange        sapphire.    -   Chromium alone produces pink or red (ruby); at least 1% chromium        for deep red ruby.    -   Iron alone produces a weak yellow or green.    -   Violet or purple sapphire is colored by vanadium.

The word “harder” when used herein refers to a relative measure of thehardness of a material when compared to another. For clarity, when afirst material or substrate that is defined as harder than a secondmaterial or substrate, the Mohs value for the first material orsubstrate will be higher than the Mohs value for the second material orsubstrate.

The word “softer” when used herein refers to a relative measure of thehardness of a material when compared to another. For clarity, when afirst material or substrate that is defined as softer than a secondmaterial or substrate, the Mohs value for the first material orsubstrate will be lower than the Mohs value for the second material orsubstrate.

The word “flexible” when used herein refers to a substrate's mechanicalproperties of being able to be physically manipulated to change itsphysical shape using force without breaking said substrate.

The word “screen” when used as a noun herein refers to a cover-glass/acover-screen/a cover-window/a display screen/a display window/acover-surface/a cover plate of an apparatus. For clarity, while in manyinstances a screen on a given apparatus has a dual function ofdisplaying an interface of the apparatus and protecting the surface ofthe apparatus, wherein for such instances good light transmittance is arequired feature of said screen; this is not a must. In other instanceswhere only the function of providing surface protection is required,light transmittance of the screen is not a must.

In one embodiment of the present invention, there is provided a methodto develop a transparent screen which is harder and better than GorillaGlass and comparable to pure sapphire screen but with the followingadvantages:

-   -   Harder than any hardened glass;    -   Less possibility of fragmentation than pure sapphire screen;    -   Lighter weight than pure sapphire screen;    -   Higher transparency than pure sapphire screen.

In one embodiment of the present invention, there is provided a methodto deposit a sapphire thin film on quartz substrate. With post-deposittreatment such as thermal annealing, an embodiment of the presentinvention has achieved top-surface hardness up to 8-8.5 Mohs, which isclose to sapphire single crystal hardness of 9 Mohs. One embodiment ofthe present invention is herein known as “Sapphire thin film on Quartz”.FIG. 2 shows the top-surface hardness of “Sapphire thin film on Quartz”when compared to ordinary glass, Gorilla Glass, quartz and puresapphire.

Quartz substrate itself is the single crystal of SiO₂ with a higher Mohsvalue than glass. Moreover, its melting point is 1610° C. which canresist high annealing temperatures. Furthermore, the substrate can becut to the desired size onto which an embodiment of the presentinvention can then deposit the sapphire thin film. The thickness of thedeposited sapphire thin film is just 1/1000 of the quartz substrate. Thecost of synthetic quartz crystal is relatively low (which is only lessUS$10/kg at the time the present invention is disclosed herein). So inan embodiment of the present invention, the fabrication cost andfabrication time is significantly reduced comparing to the fabricationof pure sapphire substrate.

Features and Benefits of One Embodiment of the Present Invention

Higher Hardness than Hardened Glass

In one embodiment of the present invention, the developed Sapphire thinfilm on Quartz has a maximum value of 8.5 Mohs in top-surface hardness.Recent Gorilla Glass used in smart-phone screen only scores about 6.5Mohs in hardness value and natural quartz substrate is 7 Mohs inhardness value. Therefore, the present invention has a significantimprovement in top-surface hardness comparing to recent technology. TheSapphire thin film on Quartz has a hardness value of 8.5 Mohs, which isvery close to pure sapphire's hardness value of 9 Mohs, and the Sapphirethin film on Quartz has the merits of lower fabrication cost andrequires a less fabrication time.

Less Fragmented, Lighter than Sapphire

In nature, the harder the materials, the more fragile they are, thus,sapphire substrate is hard to scratch but it is easy to shatter, and thevice versa is also often true. Quartz has comparatively low elasticmodulus, making it far more shock resistant than sapphire.

Moreover, in one embodiment of the present invention, the depositedsapphire thin film is very thin compared to quartz substrate wherein thedeposited sapphire thin film is only 1/1000 of the quartz substrate inthickness. Therefore, the overall weight of sapphire thin film on quartzis almost the same as quartz substrate, which is only 66.6% (or ⅔) ofthe weight of pure sapphire substrate for the same thickness. This isbecause the density of quartz is only 2.65 g/cm³ while sapphire is 3.98g/cm³ and Gorilla Glass is 2.54 g/cm³. In other words, quartz substrateis only heavier than Gorilla Glass by 4.3% but pure sapphire substrateis roughly 1.5 times heavier than Gorilla Glass and quartz. Table 1shows the comparison among the density of quartz, Gorilla Glass and puresapphire.

TABLE 1 Comparison of density of Gorilla glass, quartz and puresapphire, and their percentage differences. Materials Density DifferenceGorilla Glass 2.54 g/cm³  100% Quartz 2.65 g/cm³ 104.3% Pure Sapphire3.98 g/cm³ 156.7%

Recently published patent, i.e. U.S. patent application Ser. No.13/783,262, submitted by Apple Inc. also indicates that it has devised away to fuse sapphire and glass layers together that creates a sapphirelaminated glass to combine the durability of sapphire with the weightand flexibility advantages of glass. However, polishing a larger area(>6 inches) and thin (<0.3 mm) sapphire substrate is very challenging.Therefore, using Sapphire thin film on Quartz is the best combinationfor screen with lighter weight, higher top-surface hardness, lessfragmented substrate.

Higher Transparency than Pure Sapphire

Since the refractive index of sapphire crystal, quartz crystal andGorilla Glass are 1.76, 1.54 and 1.5 respectively, the overall lighttransmission of them are 85%, 91% and 92% due to the Fresnel'sreflection loss. That means there is a small trade-off between lighttransmission and durability. Sapphire transmits less light which canresults in either dimmer devices or shorter device battery life. Whenmore light is transmitted, then more energy is saved and the devicebattery life would be longer. FIG. 3 shows the light transmittance ofquartz, Sapphire thin film on Quartz and pure sapphire.

Most crystal, including sapphire and quartz, has birefringence problem.By comparing their refractive index for ordinary ray and extraordinaryray (n₀ and n_(e)), the magnitude of the difference Δn is quantified bythe birefringence. Moreover, the values of Δn for one embodiment of thepresent invention are also small such that the birefringence problem isnot serious for application with thinner substrate thickness (˜1 mm).For examples, pure sapphire is used as the camera cover lens in AppleiPhone 5S which there is not any blurred images reported. Table 2 showsthe refractive index of ordinary ray and extraordinary ray (n₀ andn_(e)), their differences Δn in birefringence for quartz and sapphire.

TABLE 2 Refractive indices of ordinary ray and extraordinary ray (n₀ andn_(e)), their differences Δn for quartz and sapphire. Materials Formulan₀ n_(e) Δn Quartz SiO₂ 1.544 1.553 +0.009 Sapphire Al₂O₃ 1.768 1.760−0.008

Shorter Fabrication Time and Lower Fabrication Cost than Pure Sapphire

Recently, both synthetic sapphire and quartz single crystals are grownand commercially available. Since sapphire has a higher melting pointthan quartz, the growth of sapphire is more difficult and has a highercost. More importantly, the time to grow sapphire is much longer thanquartz. Growing sapphire for larger than 6 inches products is alsochallenging and only a limited number of companies can achieve this.Therefore, it limits the production quantity such that production costof sapphire substrate is higher than quartz. Table 3 shows the formula,melting point and Mohs hardness value for quartz and sapphire.

TABLE 3 The formula, melting point and Mohs hardness value for quartzand sapphire. Materials Formula Melting point Mohs hardness Quartz SiO₂1610° C. 7 Sapphire Al₂O₃ 2040° C. 9

Another challenge in the use of pure sapphire is that sapphire crystalwith hardness value of 9 Mohs, is very difficult to cut and polish. Upto now, polishing a larger area (>6 inches) and thin (<0.3 mm) sapphiresubstrate is very challenging. The successful rate is not too high andthis prevents the price of sapphire substrate from dropping too mucheven though a larger number of sapphire crystal growth furnaces are nowin operation. Corning has claimed that sapphire screen can cost up to 10times as much as Gorilla Glass. In contrast, quartz possesses a hardnessvalue of 7 Mohs, and it is easier to cut and polish. Moreover, the costof synthetic quartz crystal is comparatively less expensive (only costsless US$10/kg at the time of the present disclosure).

Therefore, the additional cost of Sapphire thin film on Quartz is thedeposition of the sapphire thin film on the quartz substrate and thepost-treatment of the Sapphire thin film on Quartz. In one embodiment ofthe present invention, when all conditions are optimized, the process ofmass production can be fast and the cost is low.

In one embodiment of the present invention, there is provided a methodto deposit a harder sapphire thin film on quartz substrate. The thinfilm thickness is in the range of 150 nm-1000 nm. With post-deposittreatment such as thermal annealing at 500° C.-1300° C., this embodimentof the present invention has achieved hardness of 8-8.5 Mohs which isvery close to sapphire single crystal hardness of 9 Mohs. In anotherembodiment of the present invention, there is provided sapphire thinfilm with thickness of 150 nm-500 nm with an achieved hardness value of8-8.5 Mohs and also good optical performance with low scattering lost.The annealing temperature is from 1150 to 1300° C., which is very closeto sapphire single crystal hardness of 9 Mohs. FIG. 4 shows the lighttransmission of quartz and 190 nm Sapphire thin film on Quartz with andwithout annealing at 1300° C. for 2 hours. Therefore in terms ofhardness, the Sapphire thin film on Quartz is comparable to that of puresapphire screen, and its weight is almost the same as that ofglass/quartz substrate which is roughly 66.6% the weight of puresapphire substrate since the density of quartz is only 2.65 g/cm³ whilesapphire is 3.98 g/cm³. Since one can cut the substrate to the desiredsize then deposit the sapphire thin film, the fabrication cost and timeis significantly reduced comparing to that of pure sapphire substrate.

In fact, the value of hardness for sapphire thin film by e-beamdeposition is not too high. In one embodiment of the present invention,the value of hardness was measured to be less than 7 Mohs. However,after doing thermal annealing process, the thin film hardness issignificantly improved. One embodiment of the present invention hasfound that the sapphire thin film was softened as annealing at 1300° C.with 2 hours. The film thickness was shrunk about 10% and the filmhardness was improved to 8-8.5 Mohs. Since, the quartz substrate issingle crystal of SiO₂ with melting point of 1610° C., it can resist thehigh annealing temperature. Therefore, the hardness of annealed sapphirethin film on quartz substrate can attain 8.5 Mohs. FIG. 4 shows thetransmission of quartz and 190 nm Sapphire thin film on Quartz with andwithout annealing at 1300° C. for 2 hours.

Moreover, in other embodiments of the present invention, the annealingprocess of sapphire thin film was done on other substrates. Forexamples, 1000° C. annealed sapphire thin film on fused silica substrateand 500° C. annealed sapphire thin film on glass substrate, theirhardness was measured.

Electron beam (E-beam) and sputtering depositions are two most popularmethods to deposit sapphire thin film onto the quartz and other relevantsubstrates. In embodiments of the present invention, these two commondeposition methods are used.

Sapphire Thin Film by e-Beam Deposition

The summary points on sapphire thin film deposition on a given substrateby e-beam deposition is given as follows:

-   -   The deposition of sapphire thin film is using e-beam evaporation        since aluminum oxide has very high melting point at 2040° C. The        white pellets or colorless crystal in small size of pure        aluminum oxide are used as the e-beam evaporating sources. The        high melting point of aluminum oxide also allows for annealing        temperatures up to less than the melting point of sapphire (e.g.        2040° C. at atmospheric pressure).    -   The substrates are perpendicularly stuck on the sample holder        far away the evaporation source 450 mm. The sample holder is        rotated at 1-2 RPM when the deposition takes place.    -   The base vacuum of evaporation chamber is less than 5×10⁻⁶ torr        and the vacuum keeps below 1×10⁻⁵ torr when the deposition takes        place.    -   The thickness of film deposited on substrates is about 150 nm to        1000 nm. The deposition rate is about 1-5 Å/s. The substrate        during deposition is without external cooling or heating. The        film thicknesses are measured by ellipsometry method and/or        scanning electron microscope (SEM).    -   Higher temperature film deposition is possible from room        temperature to 1000° C.

A more detailed description on the process of e-beam deposition forsapphire thin film on another substrate is given as follows:

1) The deposition of sapphire thin film is using e-beam evaporationsince aluminum oxide has high melting point at 2040° C. The aluminumoxide pellets are used as the e-beam evaporation source. The highmelting point of aluminum oxide also allows for annealing temperaturesup to less than the melting point of sapphire (e.g. 2040° C. atatmospheric pressure).

-   -   2) The coated substrates are perpendicularly stuck on the sample        holder far away the evaporation source 450 mm. The sample holder        is rotated at 2 RPM when the deposition takes place.    -   3) The thickness of film deposited on substrates is about 190 nm        to 1000 nm. The deposition rate is about 1 Å/s. The substrate        during deposition is without external cooling or heating. The        film thicknesses are measured by ellipsometry method.    -   4) After deposition of sapphire thin film on substrates, they        are annealed by a furnace from 500° C. to 1300° C. The        temperature raising speed is 5° C./min and the decline speed is        1° C./min. The time is ranged from 30 minutes to 2 hours keeping        on the particular thermal annealing temperature.    -   5) The deposition substrates are including quartz, fused silica        and (toughen) glass. Their melting points are 1610° C., 1140° C.        and 550° C. respectively. The annealing temperatures of sapphire        thin film coated on them are 1300° C., 1000° C. and 500° C.        respectively.    -   6) The transmission of quartz and 190 nm sapphire thin film on        quartz with and without annealing at 1300° C. for 2 hours are        showed in FIG. 4. The light transmission percentage in whole        visible region from 400 nm-700 nm is greater than 86.7% and        maximally 91.5% at 550 nm while for pure sapphire substrate the        light transmission percentage is only 85-86%. More light        transmitted indicates more energy saved from backlight-source of        display panel, so such that the device battery life would be        longer.

Annealing Process of an Embodiment of the Present Invention

After deposition of sapphire thin film on substrates, they are annealedin a furnace from 500° C. to 1300° C. The temperature raising rate is 5°C./min and the decline rate is 1° C./min. The annealing time is from 30minutes to 2 hours maintaining at a particular thermal annealingtemperature. Multiple-steps annealing with different temperatures withinthe aforementioned range are also used to enhance the hardness and alsoreduce the micro-crack of thin film. Table 4 shows the surface hardnessand XRD characteristic peaks at different annealing temperaturesprepared by e-beam deposition. The table also shows various crystallinephases of sapphire present in the films; most common phases are alpha(α), theta (θ) and delta (δ).

TABLE 4 The surface hardness and XRD characteristic peaks at differentannealing temperatures prepared by e-beam deposition. Annealingtemperature Surface hardness XRD peaks (° C.) (Mohs) (phase) Noannealing 5.5 No 500-850 6-7 No  850-1150 7-8 theta & delta 1150-1300 8-8.5 theta & delta

Table 4 shows the changes of surface hardness of sapphire thin film as afunction of annealing temperature varies from 500° C. to 1300° C. Infact, the initial value of hardness of e-beam deposited sapphire thinfilm without annealing by is about 5.5 Mohs. However, after doingthermal annealing process, the film hardness is significantly improved.For annealing temperature in the range 500° C.-850° C., 850° C.-1150° C.and 1150° C.-1300° C., the hardness values of sapphire thin film onquartz has 6-7 Mohs, 7-8 Mohs and 8-8.5 Mohs in hardness scalerespectively.

FIG. 5 shows XRD results for the 400 nm sapphire thin film on quartzannealed at 750° C., 850° C. and 1200° C. for 2 hours. When theannealing temperature is greater than 850° C., the film starts topartially crystallize. The appearance of new XRD peaks corresponds tothe mixture of theta and delta structural phases of aluminum oxide.

When annealing above 1300° C., the film would start to develop somelarger crystallites that can significantly scatter visible light; thiswould reduce the transmission intensity. Moreover, as this largecrystallite accumulates more and more, the film would crack and somemicro-size pieces would detach from the substrate.

In one embodiment of the present invention, it was found that thesapphire thin film on quartz substrate can be annealed at 1150° C. to1300° C. within half to two hours. The film thickness would shrink byabout 10% and the film hardness is improved to 8-8.5 Mohs. Since thequartz substrate is single crystal SiO₂ with melting point of 1610° C.,it can resist such high annealing temperature. Under this annealingtemperature, the hardness of annealed sapphire thin film on quartzsubstrate has achieved 8.5 Mohs.

The light transmission of 400 nm Sapphire thin film on Quartz with andwithout annealing at 1200° C. for 2 hours are shown in FIG. 6 whilecomparing to quartz and sapphire substrates. The light transmission ofSapphire thin film on Quartz within visible region, from 400-700 nm, isgreater than 88% and maximum at 550 nm with 92%. The interferencepattern is due to the differences in refractive index of the materialsand the film thickness. The overall averaging light transmittance isabout 90% while pure sapphire substrate is only 85-86%. Moreover, thelight transmission spectrum of Sapphire thin film on Quartz coincideswith that of quartz substrate at certain wavelength which indicates theoptical performance is excellent and low scattering lost. The differencebetween maximum and minimum intensity of the interference pattern isabout 4% only. For real applications, more light transmitted indicatesmore energy saved from backlight-source of display panel, so such thatthe device battery life would be longer.

Thickness of Sapphire Thin Film on Quartz

The Sapphire thin film on Quartz with thickness in the range of 150-1000nm has been tested. In one embodiment of the present invention, there isprovided only sapphire thin film with thickness of 150 nm-500 nm havegood optical performance with low scattering lost when annealingtemperature is from 1150° C. to 1300° C. However when the thickness islarger than 600 nm, the film would crack causing significant scatteringwhich reduces the transmission intensity.

For the sapphire thin film with thickness of 150 nm-500 nm deposited onquartz after annealing at 1150° C. to 1300° C., all the measuredhardness can achieve 8-8.5 in Mohs scale which indicates that eventhinner coating film also can act as an anti-scratching layer.

Other Possible Substrates for Anti-Scratch Coating

Apart from quartz substrate, other embodiments of the present inventionhave also investigated the deposition of sapphire thin film on differentsubstrates such as fused silica and silicon. Other tempered glass ortransparent ceramic substrates with higher annealing or meltingtemperature, which can resist 850° C. annealing temperature within 30minutes to 2 hours, are also possible to use as substrates to enhancetheir surface hardness to 7-8 in Mohs hardness scale. For examples,Schott Nextrema transparent ceramics has short heating temperature at925° C.; Corning Gorilla glass has softening temperature up to 850° C.

Since the annealing temperature of fused silica is about 1160° C., it isa good candidate to start investigates its suitability as substrate.However, sapphire thin film on fused silica shows different behaviorscompared with sapphire thin film on quartz annealing from 850° C. to1150° C., even though they are deposited with same deposition condition.The adhesion of sapphire film on fused silica is not good as on quartz(or due to significant difference on the expansion coefficient),localize delamination and micro-sized crack of the film occur on fusedsilica substrate. However, using thinner film, these problems, which canlead to light scattering has greatly improved. FIG. 7 showed thetransmission of 160 nm sapphire thin film on fused silica annealed at1150° C. for 2 hours. The transmission of sapphire thin film on fusedsilica in whole visible region from 400 nm-700 nm is greater than 88.5%and maximally 91.5% at 470 nm. The overall averaging light transmittancepercentage is about 90% while pure sapphire substrate is only 85%-86%.Moreover, the measured surface hardness also maintains at above 8 inMohs scale.

Silicon, which has its melting temperature at about 1410° C., is anon-transparent substrate as substrate. From same deposition condition,sapphire film on silicon shows similar characteristics in Mohs hardnesscomparing to quartz substrate, which also divided into the two groups oftemperature range. However silicon is not a transparent substrate, thusit cannot be used as transparent cover glass or window application.Therefore, the sapphire film can only provide the anti-scratch purposeas a protection layer to protect the silicon surface from scratch(silicon has Mohs scale hardness of 7). Such protection layer canpotentially eliminate thick glass encapsulation. This would improve thelight absorption thus increase the light harvesting efficiency. Otherinorganic semiconductor-based solar cell that can withstand hightemperature treatment can also have similar deposition of the sapphirethin film onto it. From the embodiments of the present invention asdescribed herein, it is envisaged that a person skilled in the art canvery well apply the current invention to deposit sapphire thin film onto other substrates such that the sapphire thin film will act as aanti-scratch protection layer to its underlying substrate provided thesesubstrates can withstand the annealing temperatures of the currentinvention for the applicable duration of time.

Annealed Sapphire Thin Film by Sputtering Deposition

Sapphire Thin Film by Sputtering Deposition

The steps on sapphire thin film deposition on a given substrate bysputtering deposition is given as follows:

-   -   1) The deposition of sapphire thin film can be performed by        sputtering deposition using aluminum or aluminum oxide targets.    -   2) The substrates are attached onto the sample holder which is        around 95 mm away from the target. The sample holder is rotated        to achieve thickness uniformity when the deposition takes place,        example rate is 10 RPM.    -   3) The base vacuum of evaporation chamber is less than 3×10⁻⁶        mbar and the coating pressure is around 3×10⁻³ mbar.    -   4) The thickness of film deposited on substrates is about 150 nm        to 600 nm.    -   5) Higher temperature film deposition is possible from room        temperature to 500° C.

Annealing Process of Another Embodiment of the Present Invention

After deposition of sapphire thin film on substrates, they are annealedby a furnace from 500° C. to 1300° C. The temperature raising rate is 5°C./min and the decline rate is 1° C./min. The time is ranged from 30minutes to 2 hours maintaining at a particular thermal annealingtemperature. Multiple-step annealing at different temperatures are alsoused to enhance the hardness and also reduce the micro-crack of thinfilm. This is shown in Table 5.

TABLE 5 The surface hardness and XRD characteristic peaks at differentannealing temperatures for the sapphire film on quartz prepared bysputtering deposition. Annealing Surface Temperature Thickness hardnessXRD peaks (° C.) (nm) (Mohs) (phase) Transmission No annealing 6-6.5 No500-850 6-6.5 No  850-1150 340-600 Film theta & delta delamination1150-1300 150-300 8-8.5 theta & delta Low scattering 90% 300-5008.5-8.8  alpha & theta; High scattering alpha only 83-87%

Table 5 shows the changes of surface hardness of sapphire thin film onquartz as annealing temperature varies from 500° C. to 1300° C. In fact,the initial value of hardness of sapphire thin film without annealing bysputtering deposition is slightly higher than that by e-beam deposition;about 6-6.5 Mohs. After doing thermal annealing process, the performanceof film hardness is different from that by e-beam deposition. Whenannealing temperature is in the range 500° C.-850° C., the film hardnesshas no significant change. For 850° C.-1150° C. range, the thin filmcoated on quartz is easily delaminated. However, in 1150° C.-1300° C.range, the film forms hard film, with its surface hardness has 8-8.5Mohs for thickness 150 nm-300 nm and 8.5-8.8 Mohs for thicknesses 300nm-500 nm.

FIG. 8A shows XRD results for the 400 nm sapphire thin films on quartzannealing at 850° C., 1050° C. and 1200° C. for 2 hours. The occurringXRD peaks are corresponding to the mixing of delta theta and alphastructural phases of aluminum oxide. Differently from e-beamevaporation, the occurrence of alpha phase of aluminum oxide in XRDresult for sputtering deposition cause more hardened surface hardness,scoring 8.7 Mohs in average. While FIG. 8B shows XRD results for thesapphire thin film with thicknesses of 220 nm, 400 nm and 470 nm onquartz annealing at 1150° C. for 2 hours. The occurrence of alpha phasestarts from about 300 nm and when the thickness of sapphire thin filmincreases up to 470 nm, the original mixing of structural phases almostconverts to alpha phase. The surface hardness is the hardest under suchconditions. However, further increasing the thickness of sapphire thinfilm would cause film delamination.

The light transmission spectra of 220 nm, 400 nm and 470 nm sapphirethin film on quartz prepared by sputtering deposition annealing at 1100°C. for 2 hours are showed in FIG. 9 while comparing to quartz substrate.For annealed 220 nm sapphire thin film on quartz, the opticalperformance is excellent and with a little scattering lost. Thetransmission in whole visible region from 400 nm-700 nm is greater than87% and maximally 91.5% at 520 nm. The overall averaging transmittanceis about 90.2%. The difference between maximum and minimum intensity ofthe interference pattern is about 4.5% only.

However, when the thickness of sapphire thin film is greater than 300nm, the light transmittance intensity starts to drop especially in UVrange indicating that Rayleigh scattering starts to dominate. The strongwavelength dependence of Rayleigh scattering applies to the scatteringparticle with particle size, which is less than 1/10 wavelength. This isdue to the formation of alpha phase in sapphire thin film with sub-100nm crystalline size. Therefore, the surface hardness becomes harder butthe transmission becomes worse.

For annealed 400 nm and 470 nm sapphire thin film on quartz, the lighttransmission percentage in whole visible region from 400 nm-700 nm iswithin 81%-88% and 78%-87% respectively. Their overall averagingtransmittance values are about 85.7% and 83.0% respectively.

However, when the thickness of sapphire thin film is greater than 500nm, larger crystallite accumulates with micro-cracks form, the filmwould crack and some micro-size pieces would detach from the substrate.

Sapphire Thin Film on Fused Silica by Sputtering Deposition

Apart from quartz substrate, low cost fused silica is a potentialcandidate for sapphire thin film coated substrates since the annealingtemperature of fused silica is about 1160° C.

Table 6 showed the surface hardness of sapphire thin film on fusedsilica as annealing temperature varies from 750° C. to 1150° C. In fact,the initial value of hardness of sapphire thin film on fused silicawithout annealing by sputtering deposition is slightly lower than thaton quartz; about 5.5-6 Mohs. For 850° C.-1150° C. range, the hardness iseven worse, less than 5 Mohs for all 150 nm-600 nm sapphire thin films.However, at 1150° C., the film can form hard film again, which itssurface hardness has 8-8.5 for all 150 nm-600 nm sapphire thin films.

TABLE 6 The surface hardness and XRD characteristic peaks at differentannealing temperatures for the sapphire film on fused silica prepared bysputtering deposition. Annealing Surface Temperature Thickness hardnessXRD peaks (° C.) (nm) (Mohs) (phase) Transmission No annealing 5.5-6   No  850-1150 150-600 <5 theta & delta 1150-1300 150-300 8-8.5 theta &delta Low scattering 91% 300-600 8-8.5 alpha & theta; High scatteringalpha only 74-82%

FIG. 10 shows XRD results for the 350 nm sapphire thin film on fusedsilica prepared by sputtering deposition and annealing at 750° C., 850°C., 1050° C. and 1150° C. for 2 hours. XRD results show the mixing oftheta and alpha structural phases of aluminum oxide co-exist on thefused silica substrate. Therefore, the sapphire thin film has a hardsurface with 8-8.5 Mohs, whereas fused silica substrate has only scores5.3-6.5.

The transmission spectra of 180 nm-600 nm sapphire thin film on fusedsilica prepared by sputtering deposition annealing at 1150° C. with 2hours showed in FIG. 11 compared to fused silica substrate.

For annealed 180 nm and 250 nm sapphire thin film on fused silica, theoptical performance is excellent and with a little scattering lost. Thetransmission of sapphire thin film in whole visible region from 400-700nm is within 88.9%-93.1% and 84.8%-92.8% respectively. Their overallaveraging transmittance values are about 91.3% and 90.7% respectively.

For annealed 340 nm and 600 nm thick sapphire thin film on fused silica,the transmission across visible region from 400 nm-700 nm is within75%-86% and 64%-80% respectively. Their overall averaging transmittanceis about 81.7% and 74.1% respectively.

Therefore, annealed sapphire thin film on fused silica at 1150° C. withthickness of 150 nm-300 nm has good optical performance with about 91%transmittance and also has strong surface hardness with >8 Mohs.

Low Temperature Annealing Process

In current popular ‘toughened’ screen material use is Gorilla Glass fromCorning, which is being used in over 1.5 billion devices. On the Mohsscale of hardness, the latest Gorilla Glass only scores 6.5-6.8, whichis below mineral quartz such that it is still easy to scratch by sand.Therefore, there is another direction is to deposit harder thin film onglass substrate. However, for most of common used cover glass, theirallowed maximum annealing temperatures are only at the range of 600°C.-700° C. At this temperature range, the previous hardness of annealedsapphire thin film can only reach 6-7 Mohs, which is close to that ofglass substrate itself. Therefore, a new technology is developed to pushthe Mohs hardness of annealed sapphire thin film to over 7 usingannealing temperature below 700° C.

In another embodiment of our present invention, we can deposit a layeror multilayer of higher hardness thin film of sapphire onto a weakerhardness substrate with maximum allowed annealing temperature below 850°C., e.g. Gorilla glass, toughened glass, soda-lime glass and etc.Therefore, a harder anti-scratch thin film can be coated onto glass.This is the quickest way and lower cost to improve their surfacehardness.

In yet another embodiment of our resent invention, by applying anano-layer of metal, such as Ti and Ag, we have shown thatpolycrystalline sapphire thin film can be grown at lower temperature.This catalytic enhancement can be induced at temperature considerablylower than when the nano-metal catalyst is not used. The enhancementcomes from enabling crystallization established once there is sufficientkinetic energy to allow deposited atoms to aggregate and this annealingtemperature can start at 300° C. Embodiments of the present inventionwherein the low temperature annealing started from 300° C. is presentedin Table 7.

TABLE 7 Embodiments with structure of Substrate/Ti catalyst/Sapphirefilm with no annealing (Room Temperature, i.e. RT), annealingtemperatures of 300° C., 400° C. and 500° C. Sapphire Knoop IncrementSubstrate Annealing Annealing Ti catalyst film hardness in Knoop typetemperature time thickness thickness (HK0.01) hardness Fused silica RT // / 1100 / Fused silica 300° C. 2 hrs 1.5 nm 250 nm 1101  +0.09% Fusedsilica 400° C. 2 hrs 1.5 nm 250 nm 1250 +13.64% Fused silica 500° C. 2hrs 1.5 nm 250 nm 1301 +18.27% Fused silica 300° C. 2 hrs 3.0 nm 250 nm1182  +7.45% Fused silica 400° C. 2 hrs 3.0 nm 250 nm 1276 +16.00% Fusedsilica 500° C. 2 hrs 3.0 nm 250 nm 1278 +16.18% Soda lime RT / / / 788 /glass Soda lime 300° C. 2 hrs 7.5 nm 230 nm 904 +14.72% glass Soda lime400° C. 2 hrs 7.5 nm 230 nm 977 +23.98% glass Soda lime 500° C. 2 hrs7.5 nm 230 nm 1052 +33.50% glass

FIG. 13 (A) shows the X-ray reflectivity (XRR) measurement results fordifferent samples with different annealing conditions as per embodimentin Table 7, while FIG. 13 (B) shows the optical transmittance spectrafor different samples with different annealing conditions as perembodiment in Table 7.

In one embodiment, we developed a method to deposit a very thin‘discontinuous’ metal catalyst and a thicker sapphire film on glasssubstrate. With post-deposit treatment such as thermal annealing at600-700° C., we have achieved hardness of 7-7.5 Mohs, which is higherthan that of most glass.

The nano-metal catalyst should have a thickness between 1-15 nmdeposited by deposition system such as e-beam evaporation or sputtering.This catalyst is not a continuous film, as shown by SEM. The depositedmetal can have a nano-dot (ND) shape with (5-20 nm) diameter. The metalsinclude Titanium (Ti) and silver (Ag). The thicker sapphire film is inthe range of 100-1000 nm.

In fact, the hardness value of sapphire thin film by e-beam orsputtering deposition is not too high. We have measured the hardness,which is about 5.5-6 Mohs only. However, after thermal annealingprocess, the film hardness is significantly improved. Without nano-metalcatalyst, the film hardness was 6-7 Mohs with annealing temperature600-850° C. After adding the nano-metal catalyst, the film hardness hasimproved to 7-7.5 Mohs with annealing temperature 600-700° C. andachieved a hardness of 8.5 to 9 Mohs with annealing temperature701-1300° C.

This is great improvement of surface hardness on glass substrate and inparticular it is below the glass softening temperature at this annealingtemperature. This means that glass will not deform during the annealing.Thus the role of metal catalyst not only enhances the adhesion betweensapphire thin film and glass substrate but also induces the hardening ofthe sapphire thin film. The surface hardness of sapphire thin film withand without nano-metal catalyst at different annealing ranges preparedby e-beam deposition is shown in Table 8.

TABLE 8 The surface hardness of sapphire thin film with and withoutnano-metal catalyst at different annealing ranges prepared by e-beamdeposition. Annealing Surface hardness without Surface hardness withtemperature nano-metal catalyst nano-metal catalyst (° C.) (Mohs) (Mohs)No annealing 5.5 5.5-6  500/600-850 6-7  7-7.5  850-1150 7-8 7.5-8.51150-1300  8-8.5 8.5-8.8

The summary points on sapphire thin film deposited on a glass substrateby e-beam deposition are given as follows:

1) The base vacuum of evaporation chamber is less than 5×10⁻⁶ torr andthe deposited vacuum keeps below 1×10⁻⁵ torr when the deposition takesplace.

2) The substrates are attached onto the sample holder at a distance fromthe evaporation source, for example 450 mm. The sample holder is rotatedat 1-2 RPM when the deposition takes place.

3) The deposition of nano-metals with higher melting points such as Ti,Cr, Ni, Si, Ag, Au, Ge and etc., is using deposition system such ase-beam evaporation and sputtering. The thickness of metal catalystdirectly deposited on substrates is about 1-15 nm monitoring by QCMsensor. The deposition rate of nano-metal catalyst is about 0.1 Å/s. Thesubstrate during deposition is without external cooling or heating. Thefilm morphology was measured by SEM top-view and cross-section view.

4) The deposition of sapphire thin film is using e-beam evaporationsince it has very high melting point at 2040° C. The white pellets orcolorless crystal in small size of pure aluminum oxide are used as thee-beam evaporating sources. The high melting point of aluminum oxidealso allows for annealing temperatures up to less than the melting pointof sapphire (e.g. 2040° C. at atmospheric pressure).

5) The thickness of sapphire thin film deposited on substrates is about100 nm to 1000 nm. The deposition rate is about 1-5 Å/s. The substrateduring deposition is at room temperature and active temperature is notessential. The film thicknesses can be measured by ellipsometry methodor other appropriate methods with similar or better accuracy.

6) After deposition of sapphire thin film on substrates, they areannealed in a furnace from 500° C. to 1300° C. The temperature raisinggradient should be gradual for example 5° C./min and the declinegradient should also be gradual for example 1-5° C./min. The annealingtime is ranged from 30 minutes to 10 hours within the specified thermalannealing temperature range. Multiple-steps annealing with differenttemperatures within the aforementioned range can also be used to enhancethe hardness and also reduce the micro-crack of thin film.

The transmission of fused silica and 250 nm annealed sapphire thin filmwith or without 10 nm Ti catalyst on fused silica annealing at 700° C.and 1150° C. for 2 hours are shown in FIG. 12. For 700° C. annealingresult, the averaged transmission percentage in visible region from400-700 nm is greater than 89.5% and maximum of 93.5% at 462 nm whilefused silica substrate has averaged transmission of 93.5%.

Thin Film Transfer Process

In another embodiment of present invention provides a method andapparatus of fabrication of a multilayer flexible metamaterial can befabricated using flip chip transfer (FCT) technique. Such metamaterialincludes a thin film harder substrate transferred onto a softer flexiblesubstrate. This technique is different from other similar techniquessuch as metal lift off process, which fabricates the nanostructuresdirectly onto the flexible substrate or nanometer printing technique. Itis a solution-free FCT technique using double-side optical adhesive asthe intermediate transfer layer and a tri-layer metamaterialnanostructures on a rigid substrate can be transferred onto adhesivefirst. Another embodiment of the present invention is the fabricationmethod and apparatus that allows the transfer of the metamaterial from arigid substrate such as glass, quartz and metals onto a flexiblesubstrate such as plastic or polymer film. Thus, a flexible metamaterialcan be fabricated independent of the original substrate used.

Device Fabrication

A schematic fabrication process of multilayer metamaterials is shown inFIG. 14. First, the multilayer plasmonic or metamaterial device wasfabricated on chromium (Cr) coated quartz using conventional EBLprocess. The 30 nm thick Cr layer was used as a sacrificial layer. Thena gold/ITO (50 nm/50 nm) thin film was deposited onto the Cr surfaceusing thermal evaporation and RF sputtering method respectively. Next, aZEP520A (positive e-beam resist) thin film with thickness of about 300nm was spun on top of the ITO/gold/Cr/quartz substrate and a twodimensional hole array was obtained on the ZEP520A using the EBLprocess. To obtain the gold nanostructure (disc pattern), a second 50 nmthick gold thin film was coated onto the e-beam patterned resist.Finally, a two dimensional gold disc-array nanostructures was formed byremoving the resist residue. The area size of each metamaterial patternis 500 μm by 500 μm, and the period of the disc-array is 600 nm withdisc diameter of ˜365 nm.

Flip Chip Transfer (FCT) Technique

Transfer process of flexible absorber metamaterial is shown in FIG. 15,double-sided sticky optically clear adhesive (50 μm thick; e.g. acommercially available product manufactured by 3M) was attached to thePET substrate (70 μm thick). Thus the tri-layer metamaterial device wasplaced in intimate contact with optical adhesive and sandwiched betweenthe rigid substrate and the optical adhesive. Note that the Cr thin filmon quartz substrate was exposed to the air for several hours after theRF sputtering process, such that there is a thin native oxide film onthe Cr surface. Hence the surface adhesion between Cr and gold is muchweaker than that of gold/ITO/gold disc/optical adhesive bounding. Thisallows the tri-layer metamaterial nanostructure to be peeled off fromthe Cr coated quartz substrate. Once the metamaterial nanostructure wastransferred onto the PET substrate, it possesses sufficient flexibilityto be bended into various shapes. Finally, the metamaterialnanostructure was encapsulated by spin-coating a 300 nm thick PMMA layeron top of the device.

In another embodiment, the present invention provides a novel NIRmetamaterial device that can be transformed into various shapes bybending the PET substrate.

FIG. 16(a) shows the flexible absorber metamaterial sandwiched by thetransparent PET and PMMA thin film. Several absorber metamaterialnanostructures with area size of 500 μm by 500 μm were fabricated onflexible substrate. In fact, using the flexibility property of the PETlayer, the absorber metamaterial device can be conformed into many shapee.g. cylindrical shape (FIG. 16(b)). The minimum radius of thecylindrical substrate is about 3 mm, not obvious defect on themetamaterial device can be observed after 10 times of repeatable bendingtests.

Optical Characterization and Simulation

The tri-layer metal/dielectric nanostructure discussed above is anabsorber metamaterial device. The design of the device is such that theenergy of incident light is strongly localized in ITO layer. Theabsorbing effects of the NIR tri-layer metamaterial architecture couldbe interpreted as localized surface plasmon resonance or magneticresonance. The absorbing phenomenon discussed here is different from thesuppression of transmission effect in metal disc arrays, in which theincident light is strongly absorbed due to resonance anomaly of theultrathin metal nanostructure. To characterize the optical property ofgold disc/ITO/gold absorber metamaterial, fourier transform infraredspectrometer (FTIR) was used to measure the reflection spectrum of theabsorber metamaterial. By combining the infrared microscope with theFTIR spectrometer, transmission and reflection spectra from micro-areananophotonic device can be measured. In FIG. 17, the reflection spectrum(Experiment line plot) from air/metamaterial interface was measured withsampling area of 100 μm by 100 μm. At the absorption peak withwavelength of −1690 nm, reflection efficiency is about 14%, i.e. theabsorber metamaterial works at this wavelength. In RCWA simulation(Simulation line plot), the real optical constants in E. D. Palik,Handbook of optical constants of solids, Academic Press, New York, 1985is used; the content of which is incorporated herein by reference in itsentirety. At resonant wavelength, the experiment and calculation agreewell with each other.

Reflection spectrum of the flexible absorber metamaterial is shown inFIG. 18(a) (0° line plot). Compared to FTIR result in FIG. 17, theabsorption dip of the flexible metamaterial has red shifted to ˜1.81 μm.This red shift is mainly due to the refractive index change of thesurrounding medium (refractive index of optical adhesive and PET isabout 1.44). In FIG. 18(c) and FIG. 18(d), three dimensional rigorouscoupled wave analysis (RCWA) method is employed to calculate thereflection and transmission spectra on the absorber metamaterial, andexperimentally confirmed parameters of materials of gold, ITO, Cr, SiO2and PET were used Resonant absorption at wavelength of ˜1.81 μm can alsobe observed in theoretical simulations. However, there are two resonantdips around 1.2 μm in the measured reflection spectrum. In the RCWAcalculation (FIG. 18(c)), the double dips are reproduced and ascribed totwo localized resonant modes, as they are not very sensitive to incidentangles. For the angle dependent calculation, TE polarized light is used(electric field is perpendicular to incident plane) to fit theexperimental result. While the incident angle is changed from 0 to 45degree, reflection efficiency shows an increasing trend as light cannotbe efficiently localized under large angle incidence. However, the backreflection efficiency in experiment (FIG. 18(a)) decreases obviously.This is because our current experimental setup (discussed in nextsection) only allows us to collect the back-reflection signal (incidentand collection direction are same as each other), and the collectionefficiency is very low for large incident angles. In FIG. 18(b),transmission spectrum of the flexible metamaterial was measured usingthe same FTIR setup, the main difference is light was incident from theair/PMMA interface. A Fano-type transmission peak is observed atwavelength ˜1.85 μm. At resonant wavelength, the transmission efficiencyfrom experiment is higher than that in the theoretical simulation (FIG.18(d)). This could be due to defects on gold planar film and the twodimensional disc arrays, which enhances the efficiency of leakageradiation and thus contribute to the higher transmission efficiency inthe measured results.

As shown in FIG. 19, bending PET substrate allows us to measure theoptical response of absorber metamaterial under different curving shape.The shape of the bent PET substrate was controlled by adjusting thedistance between substrate ends (A and B). The angle for the resolvedback-reflection on the absorber device was measured by varying thebending conditions. From FIG. 19, the incident angle (90°-ø) wasdetermined from the bending slope at the position of the metamaterialdevice. From FIG. 18(a), it is observed that when the incident angle wasincreased from 0 to 45 degree, the intensity of the back reflectionbecomes weaker and the absorption dip becomes shallower. Nevertheless,it shows that the resonant absorption wavelength of the flexibleabsorber metamaterial is not sensitive to the incident angle of light.Devices made from the metamaterials can be made into highly sensitivesensors. This invention provides a novel technique in fabricatingmetamaterial devices on a flexible substrate. The flexibility allows thedevice to bending and stretching, which alters the device structure.Since the resonant frequency of each device is a function of the devicestructure, the resonant frequency can be tuned by the bending andstretching of the substrate. Hence, another embodiment of the presentinvention is a metamaterial that allows a physical means to change thestructure of the material, which leads to a change in its resonantfrequency. There is no need to change the material composition. Anembodiment of the present metamaterial is flexible plasmonic ormetamaterial nanostructure device used as an electromagnetic waveabsorber.

In the aforementioned embodiments of the present invention, it hasreported a highly flexible tri-layer absorber metamaterial deviceworking at NIR wavelength. By using FCT method, the tri-layer golddisc/ITO/gold absorber metamaterial was transferred from quartzsubstrate to a transparent PET substrate using optically clear adhesive(e.g. a commercially available product manufactured by 3M). Furthermore,the tri-layer absorber metamaterial was encapsulated by PMMA thin filmand optical adhesive layer to form a flexible device. FTIR experimentshowed that the absorber metamaterial works well on both the quartzsubstrate and the highly flexible PET substrate. Besides, angleinsensitive absorbing effects and Fano-type transmission resonance wereobserved on this flexible metamaterial.

Moreover, the solution-free FCT technique described in this inventioncan also be used to transfer other visible-NIR metal/dielectricmultilayer metamaterial onto flexible substrate. The flexiblemetamaterial working at visible-NIR regime will show more advantages inmanipulation of light in three dimensional space, especially when themetamaterial architecture is designed on curved surfaces. In anotherembodiment of the present invention, the FCT technique of the presentinvention can be adopted to transfer harden thin film on to a softer,flexible substrate.

Experimental Details on Transferring Thin Film onto Flexible Substrate

Method adopted in transferring Al₂O₃ thin films from rigid substrate toPET substrate is transfer through using weak adhesive metal interlayers.This approach is based on the referenced U.S. Non-Provisional patentapplication Ser. No. 13/726,127 filed on Dec. 23, 2012 and U.S.Non-Provisional patent application Ser. No. 13/726,183 filed on Dec. 23,2012, both which claim priority from U.S. Provisional Patent ApplicationSer. No. 61/579,668 filed on Dec. 23, 2011. One embodiment of thepresent invention is to use transparent polyester tape applyingmechanical stress to separate Al₂O₃ thin films altogether fromsacrificial metal layer. Then, Al₂O₃ thin film is transferred to the PETsubstrate and the sacrificial metal layer can be etched away by acid.

First, thin chromium (Cr) film (i.e. 30-100 nm-thick) is deposited ontoa fused silica substrate followed by thin silver (Ag) film (i.e. 30-100nm-thick) is deposited on top of Cr. Then another layer of metal such asTi film (3-10 nm thick) is deposited and this is for annealing process.Then, Al₂O₃ thin film (e.g. 100-500 nm) is deposited onto the metallayers. Annealing is then performed in temperature range 300° C.-800° C.as per embodiment in the low temperature annealing process of thepresent invention as disclosed earlier herein. Flexible transparentpolyester tape with optical transmission higher than 95% is attached toAl₂O₃ film and the harden Al₂O₃ thin film is mechanically peeled back.The fabrication structure is schematically illustrated in FIG. 20. Dueto different surface energies, the adhesion between Cr and Ag is weakand therefore can be easily overcome by applying stress. The appliedstress composed of both pure opening stress mode and shear stress mode.These two modes ensure that there is a clean separation between Ag andCr. Under the applied stress, the harden Al₂O₃ thin film would detachitself from the rigid substrate altogether with the sacrificial Ag layerand flexible transparent polyester tape as shown in FIG. 21. Finally,the sacrificial Ag layer is etched away by immersing the assembly asdepicted in FIG. 21 by acid such as diluted HNO₃ (1:1). Since the tapeand Al₂O₃ thin film are acid-resistant, the etchant solution would onlyetch away the sacrificial Ag layer faster. Al₂O₃ is fully transferred toPET substrate depicted in FIG. 22 after Ag thin film is completelyetched away.

Results

FIG. 23 shows the sample fabricated for transfer of Al₂O₃ thin film. Onthe fused silica substrate, Cr was first sputtered onto the substratewith a typical thickness of 50 nm at a sputtering yield at about 5nm/min. Then, 50 nm Ag was deposited on top of it by e-beam evaporation.Finally, Al₂O₃ of about 200 nm thick was deposited to the assembly bye-beam evaporation.

FIG. 24 shows the peel off of Al₂O₃ film from fused silica substrate andCr after applying mechanical peel with a transparent tape. Al₂O₃detaches from the rigid substrate completely and smoothly without anycracks and bubbles together with Ag film and tape. Al₂O₃ is successfullytransferred to the flexible PET substrate after etching away thesacrificial Ag layer in acid.

Modifications and variations such as would be apparent to a skilledaddressee are deemed to be within the scope of the present invention.

INDUSTRIAL APPLICABILITY

The present invention relates to a method to transfer a layer of harderthin film substrate onto a softer substrate, especially onto a flexiblesubstrate. In particular, the present invention provides a method totransfer a layer of sapphire thin film onto a softer flexible substratee.g. PET, polymers, plastics, paper and even to fabrics via a flip chipprocess. The combination of a layer of harder thin film sapphiresubstrate onto a softer substrate is better than pure sapphiresubstrate. In nature, the harder the materials, the more fragile theyare, thus, sapphire substrate is hard to scratch but it is easy toshatter, and the vice versa is also often true wherein quartz substrateis easier to scratch but it is less fragile than sapphire substrate.Therefore, depositing a harder thin film substrate on a softer substrategives the best of both worlds. Softer, flexible substrates are lessfragile, have good mechanical performance and often cost less. Thefunction of anti-scratch is to achieve by using the harder thin filmsubstrate.

If desired, the different functions discussed herein may be performed ina different order and/or concurrently with each other. Furthermore, ifdesired, one or more of the above-described functions may be optional ormay be combined.

Throughout this specification, unless the context requires otherwise,the word “comprise” or variations such as “comprises” or “comprising”,will be understood to imply the inclusion of a stated integer or groupof integers but not the exclusion of any other integer or group ofintegers. It is also noted that in this disclosure and particularly inthe claims and/or paragraphs, terms such as “comprises”, “comprised”,“comprising” and the like can have the meaning attributed to it in U.S.Patent law; e.g., they can mean “includes”, “included”, “including”, andthe like; and that terms such as “consisting essentially of” and“consists essentially of” have the meaning ascribed to them in U.S.Patent law, e.g., they allow for elements not explicitly recited, butexclude elements that are found in the prior art or that affect a basicor novel characteristic of the invention.

Furthermore, throughout the specification and claims, unless the contextrequires otherwise, the word “include” or variations such as “includes”or “including”, will be understood to imply the inclusion of a statedinteger or group of integers but not the exclusion of any other integeror group of integers.

Other definitions for selected terms used herein may be found within thedetailed description of the invention and apply throughout. Unlessotherwise defined, all other technical terms used herein have the samemeaning as commonly understood to one of ordinary skill in the art towhich the invention belongs.

While the foregoing invention has been described with respect to variousembodiments and examples, it is understood that other embodiments arewithin the scope of the present invention as expressed in the followingclaims and their equivalents. Moreover, the above specific examples areto be construed as merely illustrative, and not limitative of thereminder of the disclosure in any way whatsoever. Without furtherelaboration, it is believed that one skilled in the art can, based onthe description herein, utilize the present invention to its fullestextent. All publications recited herein are hereby incorporated byreference in their entirety.

Citation or identification of any reference in this section or any othersection of this document shall not be construed as an admission thatsuch reference is available as prior art for the present application.

What we claim is:
 1. A method for transferring a sapphire (Al₂O₃)coating from a first substrate to a second substrate comprising; atleast one first deposition process to deposit at least one first thinfilm onto at least one first substrate to form at least one first thinfilm coated substrate; at least one second deposition process to depositat least one second thin film onto the at least one first thin filmcoated substrate to form at least one second thin film coated substrate;at least one third deposition process to deposit at least one catalystonto the at least one second thin film coated substrate to form at leastone catalyst coated substrate; at least one fourth deposition process todeposit at least one sapphire (Al₂O₃) thin film onto the at least onecatalyst coated substrate to form at least one sapphire (Al₂O₃) coatedfirst substrate; at least one annealing process, wherein said at leastone sapphire (Al₂O₃) coated first substrate is annealed under anannealing temperature ranging from 300° C. to less than a melting pointof sapphire (Al₂O₃) for a time to form at least one hardened sapphire(Al₂O₃) thin film coated first substrate; attaching at least one secondsubstrate to the at least one hardened sapphire (Al₂O₃) thin film coatedfirst substrate on a surface of the at least one hardened sapphire(Al₂O₃) thin film to form a bond between the at least one secondsubstrate and the at least one hardened sapphire (Al₂O₃) thin filmcoated first substrate; at least one mechanical detachment processdetaching the at least one hardened sapphire (Al₂O₃) thin film togetherwith the at least one second thin film from the at least one first thinfilm coated substrate to form at least one second thin film coatedhardened sapphire (Al₂O₃) thin film on said at least one secondsubstrate; and at least one etching process removing the at least onesecond thin film from the at least one second thin film coated hardenedsapphire (Al₂O₃) thin film on said at least one second substrate to format least one sapphire (Al₂O₃) thin film coated second substrate.
 2. Themethod according to claim 1, wherein said at least one first substrateand/or said second substrate comprises at least one material with a Mohsvalue less than that of the at least one sapphire (Al₂O₃) thin film. 3.The method according to claim 1, wherein said at least one first orsecond or third or fourth deposition process comprises e-beam depositionor sputtering deposition.
 4. The method according to claim 1, wherein athickness of said at least one first substrate and/or said at least onesecond substrate is of one or more orders of magnitude greater than thethickness of said at least one sapphire (Al₂O₃) thin film.
 5. The methodaccording to claim 1, wherein the thickness of said at least onesapphire (Al₂O₃) thin film is about 1/1000 of the thickness of said atleast one first substrate and/or said at least one second substrate. 6.The method according to claim 1, wherein said at least one sapphire(Al₂O₃) thin film has the thickness between 150 nm and 600 nm.
 7. Themethod according to claim 1, wherein said time is no less than 30minutes.
 8. The method according to claim 1, wherein said time is nomore than 2 hours.
 9. The method according to claim 1, wherein saidannealing temperature ranges between 850° C. and 1300° C.
 10. The methodaccording to claim 1, wherein said annealing temperature ranges between1150° C. and 1300° C.
 11. The method according to claim 1, wherein thefirst substrate comprises quartz, fused silica, silicon, glass, ortoughened glass, and the second substrate comprises PET, polymers,plastics, paper and/or fabric wherein the second substrate is notetch-able by the at least one etching process.
 12. The method accordingto claim 1, wherein the bond between said at least one substrate andsaid at least one hardened sapphire (Al₂O₃) thin film is stronger thanthe bonding between said at least one first thin film and said secondthin film.
 13. The method according to claim 1 wherein the at least onefirst thin film comprises chromium (Cr) or a material that forms aweaker bond between the at least one first thin film and the at leastone second thin film further wherein said material for the first thinfilm is not etched by the at least one etching process that etches thematerial for the second thin film.
 14. The method according to claim 1wherein the at least one second thin film comprises silver (Ag) or amaterial that forms a weaker bond between the at least one first thinfilm and the at least one second thin film further wherein said materialfor the second thin film is etched by the at least one etching process.15. The method according to claim 1, wherein said at least one catalystcomprises a metal selected from titanium (Ti), chromium (Cr), nickel(Ni), silicon (Si), silver (Ag), gold (Au), germanium (Ge) or a metalwith a higher melting point than the at least one first substrate. 16.The method according to claim 1, wherein said at least one catalystcoated substrate comprises at least one catalyst film.
 17. The methodaccording to claim 16, wherein said at least one catalyst film is notcontinuous.
 18. The method according to claim 16, wherein said at leastone catalyst film has a thickness ranging between 1 nm and 15 nm. 19.The method according to claim 16, wherein said at least one catalystfilm comprises a nano-dot with a diameter ranging between 5 nm and 20nm.